Bushing drivers can be fabricated from just about anything with a wide flat surface and some sort of a handle on it, such as old engine valves.
A good bushing driver set is not inexpensive, and really not needed if you are only doing one or two units. Most bushings are driven in flush, so any suitable driver with a broad flat surface and some sort of a handle works. For bushings that are driven in below flush, you can split an old bushing and use it in combination with a flat driver. Complete bushing driver sets, as shown here, have the necessary drivers to set any bushings to specific depth.
Some bushings are driven in below flush. They may be, for example, deep enough that they are below the lube oil supply hole. Careful measurement and care must be used to install these bushings to the same depth at which they were originally installed. This requires a bushing driver slightly smaller than the hole into which the bushing is driven. If a bushing is located in a blind hole, it may be difficult to remove. A sharp punch ground on a slight angle can be fabricated to catch the edge of the bushing and drive it down. The bushing turns sideways in the bore and can then be pried out with a large screwdriver.
The lower case bushings for the TH350 and TH400 transmissions should be driven in from the front. You need an extension with a suitable bushing driver to gain access to them.
A long tapered punch is a must for bushing removal. Grind an angle to the tip as shown. The sharp edge catches the bushings and helps remove them from their bore. Even bushings in blind holes can be turned sideways and pried out using a tapered punch.
Instead of using a tapered punch, you can remove the TH350’s output shaft bushing with a starting tap. Thread the tap into the bushing and continue until it hits the bottom of the bore. It pushes the bushing out of the bore without damaging anything.
The lower case bushings on TH350s and TH400s may require a long extension to drive the new bushing in place. You need a large piece of solid steel pipe to help drive them in. The front output shaft bushing in the TH350 transmission can be effectively removed with a large tap. Tap the bushing and continue to turn the tap until it hits the bottom of the hole; it pushes the bushing out of the output shaft. This bushing is difficult to remove by any other method.
Use a large punch ground at an angle (as described above) to remove this bushing. You need a shop vise with soft jaws to effectively hold the output shaft. With a hammer and angle-ground punch, drive down on the edge of the bushing. Locate the seam if possible, and collapse the bushing; it can then be removed from the output shaft. Use care for this procedure to avoid damaging the inside of the bore where the bushing is located.
Heli-Coils and Bolt Extractors
The transmissions that I discuss here are cast aluminum alloy. Steel fasteners attach the various parts, such as the vacuum modulator and oil pan. It is not uncommon to strip the threads out of the case in one or more places; this usually occurs with the oil pan attaching bolts. In some cases, a longer bolt can be used to reach new threads. Another option is to use a larger-diameter bolt.
However, the best repair is to install a thread insert into the case. This repair is stronger than the original material. Several companies make threaded-insert kits. They come with a tap, several threaded inserts, and a special tool to install them.
It’s almost certain that one or more bolt holes for the oil pan will require a Heli-Coil or other thread insert. They are easy to install, and the end result is stronger and holds better than the original material.
Air tools are helpful in transmission rebuilding. They can speed up the time considerably that is needed to install and remove fasteners. High-pressure compressed air is also necessary to bench-test clutch packs and other components during the rebuilding process.
A blowgun with a long tip is essential to access small holes in the case, oil pump and clutch drums to air test them. A rubber tip or shop rag can be used to help seal off the air to listen for any leakage at the newly installed seals. The blowgun can also be used to dry off parts, and blow dirt off of the case during cleaning.
Another big advantage of having compressed air available is cleaning gasket surfaces. You can equip a high-speed air grinder with abrasive discs to remove stubborn gasket material and gasket sealers. The discs are available in several varieties; the finer ones remove gasket material and will not damage the aluminum surface where the gasket seals.
Heli-Coil Installation
The Heli-Coil is very easy to install and takes only a little practice. The repair is stronger than the original material. In most cases, it is not necessary to drill out the old threads to start the Heli-Coil tap. Make sure that the tap is perpendicular to the mounting surface when it starts into the hole. Check the angle of the tap from several views to make sure that it is straight. Go slowly; a few drops of light oil or ATF helps the tap cut the threads cleanly. Tap deeply enough to accommodate the threaded insert or tap all the way to the bottom of the hole if it is a blind hole.
The most likely place a Heli-Coil installation is needed is on the oil pan rail. Most TH350s have had several fluid changes in their lifetime and at least one of the pan rail bolt holes will have stripped threads. In most cases, it is not necessary to drill out the hole to get the Heli-Coil tap started.
Tap the hole for the Heli-Coil deep to accommodate the threaded insert. Install the insert just below flush with the surface. Some bolt holes go all the way through; you may have to shorten the insert by a few coils so it is contained completely inside the hole and not sticking out on either end.
Once the insert is installed to the correct depth, remove the small bent end at the bottom and then remove the broken-off piece from the hole. The inserts have a small break on the first coil so the bottom of the insert breaks off easily without disturbing the rest of the coils.
Once the thread insert is correctly installed, it is stronger than the original aluminum material. Test fit a correct bolt into the hole; it should go all the way through the insert with minimal effort.
Blow out all the chips from the tapping process and insert the Heli-Coil insert with the tool provided. Be sure to insert the Heli-Coil insert about one thread below the flat surface so it has good purchase in the hole and doesn’t try to come out when the fastener is tightened. Use the provided tool to break off the bottom of the Heli-Coil; remove the small piece from the hole before you install the fastener.